1. Field of the Invention
The present invention relates to the supplying of preset quantities of fluids, particularly viscous liquids such as lubricants.
2. Background and Related Information
At present, there are no systems for the reliable (i.e., precise) and accurate supply of measured quantities of liquids, such as hydrocarbons, to a customer or user preselecting a bulk quantity of the liquid. It is desirable to provide for the delivery of preselected, measured, bulk quantities of liquids in a manner which is precise and accurate enough to comply with the regulations concerning distribution of liquids for public use.
Regulations concerning apparatuses for supplying preselected quantities of liquids require that the difference between the desired quantity of the liquid and the delivered quantity of the liquid (which is used for quoting the price the buyer will have to pay), should not exceed a ratio set at five parts per thousand. In most cases, known apparatuses exceed this accuracy threshold, and also vary to a great extent for identical preselected quantities (i.e., lack precision in repeatedly supplying a given quantity of a liquid).
U.S. Pat. No. 4,442,953 discloses an apparatus for supplying preselected quantities of fluids, particularly hydrocarbons. The apparatus comprises a pump driven by a motor, a flow meter mounted downstream of the pump, and a control circuit. The flow meter generates a number of electric pulses proportional to the quantity of liquid passing through the flow meter. The control circuit is connected to both the motor and the flow meter. This apparatus is designed to ensure that the preselected quantity is actually delivered.
In the operation of this apparatus, before the apparatus is set to work, a curve showing an oversupply quantity of liquid is drawn. The shape of the curve depends upon the flow quantity indicated by the flow meter. The curve is taken as a compensating reference for the pump inertia. The curve is stored in the control circuit. During delivery of the fluid, for each measured quantity preset by a user, the circuit counts the number of pulses generated by the flow meter. When this count reaches a value equal to the number of pulses which coincides with the preset quantity minus the number of pulses corresponding to the flow quantity measured by the flow meter according to the stored reference curve, the motor of the pump is then deactivated (i.e., stopped).
However, this apparatus does not guarantee the accuracy of measured quantities of delivered liquids. This is because the reference curve is valid only for the conditions of its calculation. These conditions are not necessarily the same for future deliveries of liquids, due to variations in the temperature of the liquid, which generates variations in the viscosity of the liquid, the speed of the pump driving motor, and in the liquid manometric lift, particularly in the tank.
Such apparatuses do not always meet the minimum legal requirements (i.e. .ltoreq.0.5%), and are unfit for supplying preset quantities of viscous liquids, particularly lubricants, since their higher viscosity generates flow variations which are much higher than the flow variations of non-viscous or slightly viscous hydrocarbon liquids.
PCT Application WO-A-8604572 discloses a system for reliably and accurately supplying preset small quantities of a liquid. More specifically, this system is designed for adjusting the quantity of liquid of a photographic developer bath. The system operates by establishing the difference between the measured quantity and the quantity actually delivered for each delivery, and rectifies the following delivery accordingly.
Such a method by no means guarantees an accurate measuring of the quantity delivered, since the quantity is not readjusted, an operation which, in any event, cannot be performed, the difference observed simply being integrated to the next delivery.